Coal liquefaction using high and low boiling solvents

ABSTRACT

First and second slurries of a particulate coal are formed with low and high boiling fractions of a coal-derived solvent boiling within the range from 300* to 1,000* F., the cut point of the two fractions being from about 500* F. to about 600* F. The slurries are separately liquefied, producing a higher total cylcohexane conversion of the coal than if the coal had been slurried instead in the total coal-derived solvent and liquefied under like conditions.

Keller et al. 1 Apr. 10, 1973 [54] COAL LIQUEFACTION USING HIGH2,658,861 11/1953 Pevere et a] ..208/8 AND ow BOILING SOLVENTS 3,535,22410 1970 Corey et al. ....208/8 3,583,900 6/1971 Gatsis ..208/8 [75]Inventors: John E. Keller, Baytown, Tex.; Jack Hochman, Boonton, Ni;James Primary ExaminerDelbert E. Gantz Q- 'a Baytown, AssistantExaminerVeronica OKeefe [73] Assigneez Esso Research and EngineeringAttorneyThomas B. McCulloch, Melvin F. Fincke,

Company, Linden NJ John S. Schneider and Sylvester W. Brock, Jr.

[22] Filed: Mar. 3, 1971 [57] ABSTRACT PP 120,437 First and secondslurries of a particulate coal are formed with low and high boilingfractions of a coalderived solvent boilin within the ran e from 300 toUS. Cl ..20s 8 g g Int Cl Clog 6 1,000 F., the cut point of the twofractions being [58] Fieid 208/8 from about 500 F. to about 600 F. Theslurries are Separately liquefied, producing a higher total y [56]References Cited cohexane conversion of the coal than if the coal hadbeen slurried instead in the total coal-derived solvent UNITED STATESPATENTS and liquefied under like conditions.

1,864,496 6/1932 Pier et a1. .208/8 14 Claims, 1 Drawing Figure IPRODUCT LIOUEFACTION 22 REACTORS LIQUID PRODUCT LIQUID PRODUCT LIQUIDCOKER FRACTIONATOR f" SOLVENT 11101015111110" REACTORS FURNACE PATEHTEDAPR 1 01973 JA MES i1. FOSTER JOHNE KELLER, JACK M HOCHMAN,

INVENTOR'S AT ORNEY :3 3; I Z w 6 0 Q H h {r o l: g :3 9

3 283: 222582; m 5:3 I 223: 3 a k 22:: as: 2 $2255 i 1:: 522: N? A 5m 2A|L| l 22E 3 T on r812; N L Lynn-00 COAL LIQUEFACTION USING HIGH AND LOWBOILING SOLVENTS BACKGROUND OF THE INVENTION This invention relates tothe solvent liquefaction of coal in a coal liquid solvent, and moreparticularly, it involves the separate liquefaction of two slurries ofthe like coal, one slurry being formed with a high boiling coal liquidsolvent and the other with a low boiling coal liquid solvent.

DESCRIPTION OF THE PRIOR ART Normally in the solvent liquefaction ofcoal, particulate coal is heated in liquefaction reactors at elevatedtemperatures while slurried in a coal-derived solvent boiling widely atleast within a range from 400 to 850 F., usually to as low as about 300F. to as high as about l,000 F. The solvent normally is hydrogenatedeither before preparation of the slurry or in situ in the liquefactionreactor, or by both procedures, so that it contains hydrogen-donormolecules when in the liquefaction reactor. Hydrogen-donor moleculeshave the ability to donate hydrogen to the liquids being made from thecoal at the elevated temperatures in the.

liquefaction reactors. Liquids are made from the coal when weakerchemical bonds in the very large coal molecules are thermally cracked.As ameasure of coal liquefaction, cyclohexane conversionthe weightpercent of moisture and ash-free (MAF) coal that is converted tomaterials soluble in cyclohexane-is considered representative of theextent to which MAF coal is converted to liquids boiling below about1,000 F.

SUMMARY OF THE INVENTION Surprisingly, we have discovered that byforming separate slurries of a coal, one in a low boilingv coalderivedsolvent and the other in a high boiling coalderived solvent, and thenseparately liquefying the separate slurries, a total cyclohexaneconversion of the coal is obtained which is greater than that whichoccurs when the coal is slurried in a single wide boiling coalderivedsolvent and liquefied under like liquefaction conditions. I I

Briefly, then, our invention involves a process for liquefying coal inwhich a first slurry of a particulate coal is formed with a low boilingcoal-derived solvent having an initial boiling point of at least about300 F. and a final boiling point within the range from about 500 F. toabout 600 F., and in which a second slurry of the coal is formed with ahigh boiling coal-derived solvent having an initial boiling point withinthe range from about 500 F. to about 600 F. and a final boiling point nohigher than about 1,000" F., the final boiling point of the low boilingsolvent and the initial boiling of the high boiling solvent beingsubstantially the same. The first and second slurries are thenseparately liquefied under predetermined liquefaction conditions. Theselection of the temperature between 500 F.

and 600 F. which demarcates the low boiling coalderived solvent from thehigh boiling coal-derived solvent is advantageously made so thatsubstantially all two-ring hydrocarbonaceous compounds derived from thecoal are in the low boiling solvent while substantially all of thethree-ring or higher hydrocarbonaceous compounds derived from the coalare in the high boiling solvent. Accordingly, the demarcationtemperature separating the low boiling coal-derived solvent from thehigh boiling coal-derived solvent is preferably within the range fromabout 500 F. to about 550 F.

Separate liquefaction products with improved cyclohexane conversions areproduced by separately liquefying the first and second slurries. Atleast the liquids in the separate liquefaction products are combined andfractionated to obtain liquid product boiling in desired ranges. The lowboiling coal-derived solvent and the high boiling coal-derived solventpreferably are recycle streams recovered by fractionating the combinedliquids in the two liquefaction products. The cut point in thefractionation for recovering a low boiling coal-derived recycle solventand a high boiling coalderived recycle solvent is accordingly within therange from about 500 F. to about 600 F., preferably from about 500 F. toabout 550 F.

When using recycled solvents for the low and high boiling coal-derivedsolvents, it is necessary to recover the two solvents from the combinedliquids obtained from the separate liquefactions of the separateslurries,

in order to maintain solvent balance. The net production of high boilingcoal liquids in the liquefaction of the slurry made with a high boilingcoal-derived recycle solvent is insufficient to permit the continuedrecycle, without makeup, of a high boiling coal-derived solventrecovered by fractionation of the liquids produced on liquefying thehigh boiling solvent slurry. The same is true of the liquids produced onliquefying the low boiling solvent slurry.

The liquid product stream, which preferably is fractionated toseparately recover a low boiling coal liquid recycle solvent and a highboiling coal liquid recycle solvent, may boil, e.g., from about 400 F.to about 700 F. The composition of the equilibrium liquid product streamwill vary somewhat, depending upon the source of the coal used as thefeedstock to the system and the operating conditions in the liquefactionzone. However, a typical description of a liquids product stream which,in this case is hydrogenated, will be similar to that shown in Table I.

TABLE I Solvent Properties Typical Solvent Distillation CumulativeVolume Percent Vaporized Temperature, F.

400 Initial Cut Overall specific gravity [.0350

Solvent Elemental Composition Element Weight Percent Carbon 9 l .23Hydrogen 7.67 Nitrogen 0.48 Sulfur 0.05

With a cut point of 550 F., a typical description of a hydrogenated lowboiling coal-derived recycle solvent and that of a typical hydrogenatedhigh boiling coalderived solvent will be similar to those shown inTables 11 and III.

TABLE 11 400l550 F. Solvent Properties Specific Gravity 1.0078

Elemental Composition Element Weight Percent Carbon 91 .03

Hydrogen 8.03

Nitrogen 0.5 1

Sulfur 0.01

TABLE III 5 50/700 F. Solvent Properties Specific Gravity 1.0703

Elemental Composition Element Weight Percent Carbon 91.48 Hydrogen 7.23Nitrogen 0.44 Sulfur 0.09

The low boiling coal-derived solvent, which can have a hydrogen contentas low as about 6 weight percent, and the high boiling coal-derivedsolvent, which can have a hydrogen content as low as 5 weight percent,suitably are hydrogenated to add from about 0.1 to about 5, preferablyfrom about 0.2 to about 2, weight percent of hydrogen to them,hydrogenation being regulated so that the low boiling coal-derivedsolvent contains up to about 10.5 weight percent hydrogen, preferablyfrom about 7.5 to about 9.5 weight percent hydrogen, and the highboiling coal-derived solvent has a hydrogen content up to about 9.5weight percent, preferably from about 7 to about. 9 weight percent.

Where, as preferred, the low boiling and high boiling coal-derivedsolvents are recycle streams recovered by fractionating the combinedliquids from the separate liquefaction reactors, the hydrogenation maybe conducted on a combined liquid products stream before such stream isfractionated to recover the low and high boiling coal-derived recyclesolvents, or on the low and high boiling coal-derived recycle solventsafter fractionation of a combined liquid products stream, or in situ inthe liquefaction reactor where liquefaction conditions include ahydrogen treat rate of from about 0.1 to about 6 weight percent hydrogen(MAF coal). Hydrogen-donor compounds present in the low boilingcoal-derived recycle solvent as a result of hydrogenation includewithout limitation one or more of such two-ring compounds as indane,tetrahydronaphthalene,

mcthyltetrahydronaphthalene and dimethyltetrahydronaphthalene.Hydrogen-donor compounds present as a result of hydrogenation in thehigh boiling coal derived solvent include, without limitation, one ormore of such three-ring compounds as tetrahydroacenaphthene,acenaphthene, methylacenaphthene, octahydroanthracene,tetrahydroanthracene and dihydroanthracene.

In preparing the slurry fed to the liquefaction zone, the coal feedstockused to form two slurries is a solid particulate coal such as abituminous coal, sub-bituminous coal, lignite, brown coal, or a mixturethereof. Although it is desirable to grind the coal to a particle sizedistribution of from about 8 mesh (Tyler) and smaller, it has been foundthat the coal suitably liquefies even in particles as large as onefourth inch on the major dimension are in a slurry. A typical proximateand ultimate analysis of a suitable high volatile bituminous coal is setforth in Table [V which follows:

Preferably the coal is dried to remove excess water, either byconventional techniques or preferably by mixing the moisture containingcoal with a hot low or high boiling coal-derived solvent to volatilizewater therefrom. Moisture in the resultant slurry preferably is lessthan about 2 weight percent.

The low and high boiling coal-derived solvents are separately suitablymixed with the particulate coal in a solvent-to-coal ratio of from about0.8:] to about 2:1, preferably about 1.221. The slurry prepared with thelow boiling solvent, which has a higher volatility than the high boilingsolvent, suitably is prepared at a slightly higher solvent-to-coal ratiothan the slurry prepared with the high boiling solvent, so as to maintain a selected solvent-to-coal ratio, e.g., 1.2:1, in the liquefactionreactor, where more of the lower boiling solvent will be in the vaporstate.

Each of the separate slurries, the one prepared with the low boilingsolvent and the other prepared with the about 0.1 to about 6 weightpercent (MAF coal).

Liquefaction conditions in the separate reactors suitably may differ tooptimize the liquefactions occurring in the different solvents.

The invention will be better understood byreference to the followingdetailed description of a preferred embodiment of it, which is depictedin the drawing.

DESCRIPTION OF THE DRAWING The drawing is a schematic flow'diagram of acoal liquefaction process conducted in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a highboiling coal-derived solvent recycle stream and a low boilingcoalderived solvent recycle stream 12 are recovered, respectively, fromsolvent hydrogenation reactors 52 and 54. The high boiling stream fromline 10 suitably initially boils within the range from about 500 F. toabout 600 F., e.g., about 550 F., and has a final boiling point of up toabout l,000 F., suitably 700 F. The low boiling solvent recycle streamfrom line 12 suitably initially boils as low as about 300 F., e.g., 400F., and termally boils within a range from about 500 F. to about 600 F.,e.g., about 550 F. The low boiling solvent recycle stream in line 12 ismixed with a particulate coal, suitably 8 mesh (Tyler) and smaller, fromline 16, at a solvent-to-coal ratio suitably within the range of about0.8:1 to 2:1, e.g., about 1.3, to produce a first slurry. The highboiling solvent recycle stream from line 10 is separately mixed with alike coal, also suitably an 8 mesh (Tyler) and smaller, from line 14 ata solvent-to-coal ratio also suitably within the range from 0.811 to 2:1e.g., about 1.2, to produce a second slurry stream. The first and secondslurry streams are then conducted into furnace 18, where they arepreheated to a temperature suitably within the range from 700 F. to 950F., preferably from about 750 F. to about 850 F. The preheated secondslurry stream is then led by line 20 into liquefaction reactor 24, andthe preheated first slurry stream is carried by line 22 intoliquefaction reactor 26. In the separate liquefaction reactors, thefirst and second slurries are separately liquefiedunderliquefactionconditions suitably including a temperature within the rangefrom about 700 F. to about 950 F., preferably from about 750 F. to about850 F., and a pressure suitably within the range from about 300 psig toabout 3,000 psig, preferably from about 300 psig to about 2,500 psig.Preferably, hydrogen is introduced into liquefaction reactors 24 and 26so as to provide a hydrogen treat rate within the liquefaction reactorswithin the range from 0.1 to about 6 weight percent (MAF coal) toreplenish hydrogen depleted hydrogen-donor molecules in the solvents.

After a suitable residencetime, e.g., from about 5 minutes to about 60minutes, vaporous and gaseous materials are removed overhead fromliquefaction reactors 24 and 26 by way of lines 34 and 36, respectively,for treatment to recover them in separate streams. Separate liquidliquefaction products comprised of a mixture of undepleted hydrogendonor solvent, depleted hydrogen donor solvent, dissolved coal,undissolved coal and mineral matter are recovered from reactors 24 and26, respectively, by lines 28 and 30. Lines 28 and 30 are then combinedand charged to a fluid coker 40, which is preferably operated with adense phase bed of coker particles maintained in fluidized state bysteam and by evolution of vapor volatilization and cracking of thecharge stream, as known in'the art. Within the fluid coker 40, theliquid hydrocarbons from line 32 undergo thermal cracking to producevarious products which pass upwardly, usually through a cyclone-typeseparator (not illustrated), which returns coker particles back to thefluidized bed and permits the vaporous particles to ascend upwardly intoa coker fractionator which is suitably mounted atop the fluid coker. Inthe coker fractionator, the vaporous products are liquefied anddistilled according to boiling point. A liquid product boiling above thedesired cut point for the solvent is suitably withdrawn by way of line42, as product or for further upgrading. A heavy fraction, preferablyboiling from about 550 F. to about 700 F., is withdrawn by way of line44, suitably as liquid product, but at least in part, preferably for useas high boiling coal-derived recycle solvent. Similarly, a low boilingfraction, preferably boiling from about 400 F. to about 550 F., iswithdrawn by way of line 46, suitably as liquid product, but at leastpartially, preferably for use as a low boiling coal-derived recyclesolvent.

To upgrade its hydrogen content, the heavy solvent fraction in line 44is carried by way of line 48 into a catalytic solvent hydrogenationreactor 52. Similarly, the low boiling solvent fraction in line 46 iscarried by way of line 50 into a catalytic solvent hydrogenation reactor54 for the same purpose. Hydrogenation conditions maintained in solventhydrogenation reactors 52 and 54 suitably include a nondestructive(i.e., noncracking) temperature within the range from about 650 F. toabout 850 F., preferably about 700 F., and pressures suitably within therangefrom about 650 psig to about 2,000 psig, preferably about 1,300psig. Hydrogen is admixed with streams 48 and 50, respectively, by wayof lines 49 and 51 in sufficient excess to provide a total hydrogentreat rate in the reactors within the range from about 1,000 to about10,000, preferably up to about 5,000, standard cubic feet of hydrogenper barrel of total feed to each reactor.

The hydrogenation catalysts employed in reactors 52 and 54 are ofconventional nature. Without being limited to any particular catalyst,these catalysts will typically comprise an alumina or silica-aluminasupport carrying one or more iron group metals and one or more metals ofGroup VI-B of the Periodic Table in the form of the oxides or sulfides.In particular, combination of one or more Group VI-B metal oxides ofsulfides with one or more Group VIII metal oxides or sulfides arepreferred. For example, typical catalyst metal combinations contemplatedare oxides and/or sulfides of cobalt-molybdenum, nickel-tungsten,.nickel-molybdenum-tungsten', cobalt-nickel-molybdenum, nickelmolybdenum, etc. As a typical example, one catalyst will comprise a highmetal-content sulfided cobaltmolybdenum-alumina catalyst containingabout 1 to 10 weight percent cobalt oxide and about 5 to 40 weightpercent molybdenum oxide, especially about 2 to 5 weight percent cobaltand about 10 to 30 weight percent molybdenum. It will be understoodthatother oxides and sulfides will be useful, such as those of iron,nickel, chromium, tungsten, etc. The preparation of these catalysts isnow well known in the art..The active metals can be added to therelatively inert carrier by impregnation from aqueous solutions followedby drying and calcining to activate the composition. Suitable carriersinclude, for example, activated alumina, activated alumina-silica,zirconia, titania, etc., and mixtures thereof. Activated clays, such asbauxite, bentonite and montmorillonite, may also be employed.

A high boiling coal-derived recycle solvent stream having a hydrogencontent no greater than about 9.5 weight percent is recovered fromreactor 52 by way of line 10, and a low boiling coal-derived solventrecycle stream having a hydrogen content no greater than about 10.5weight percent is recovered from reactor 54 by way of line 12. Each ofthe streams is then recycled to form separate slurries, as hereinbeforedescribed.

The following example will demonstrate the unexpected increases incyclohexane conversion obtained with the present process. Cyclohexaneconversion is calculated by the equation:

% Conversion [S,S (100)]/[S,(l 0.0l

wherein a ash in the moisture-free coal feedstock S,= solids in the feedslurry, and

S, solids in the product slurry. Before measuring S cyclohexane is addedto the product slurry as solvent, in the ratio of one volume per eachvolume of product slurry.

EXAMPLE Base Case: Liquefaction Using Total Solvent Using twohydrogenated creosote oils normally boiling from 400 F. to 700 F., afirst having a hydrogen content of 7.67 weight percent and the second ahydrogen content of 8.42 weight percent, two slurries of Illinois No. 6coal were prepared at a solvent-to-coal ratio of 1.2:1. Each slurry wasintroduced into a liquefaction reactor and subjected to a temperature of775 F. and a pressure of 350 psig in contact with 0.3 weight percenthydrogen gas for a residence time of 30 minutes. Identical such slurrieswere identically liquefied several times. The cyclohexane conversion ofthe slurry prepared with the first 400l700 F. solvent was an average23.9 weight percent (MAF coal), and that of the slurry prepared from thesecond 400/700" F. solvent was an average 35.2 weight percent (MAFcoal).

Split Solvent Liquefaction Case One: Solvent No. l

The first 400/700 F. solvent was fractionated into a low boiling 400/ 50F. cut and a high boiling 550/700 F. cut. The low boiling cutconstituted about 49 volume percent of the 400/700 F. solvent andcontained 8.03 weight percent hydrogen. The high boiling cut was 51volume percent of the total solvent and had a hydrogen content of 7.23weight percent. A slurry of Illinois No. 6 coal was prepared with eachcut at l.2:l solvent-tocoal ratio, and each slurry was introduced intoseparate liquefaction reactors where each was subjected to the sameliquefying conditions used in the base case. identically prepared firstand second slurries were subjected to like liquefactions in severalrepeat experiments. The cyclohexane conversion of the slurry preparedwith the 400/550 C. cut was an average 37.8 weight percent (MAF coal)and that of the slurry prepared with the 550/700 F. cut was an average30.0 weight percent (MAF coal). Case Two: Solvent No. 2

Again using a cut point of 550 F., the second 400/700 F. solvent wasfractionated into low and high boiling fractions, the low boilingfraction constituting about 52 volume percent of the total solvent andthe high boiling fraction being about 48 volume percent thereof. Thehydrogen content of the low boiling fraction was 8.78 weight percent,and that of the high boiling fraction was 8.01 weight percent. As inCase One, slurries were formed with each fraction at solvent-tocoalratios of 1.2:1, and the slurries were liquefied under the base caseconditions. Identically prepared first and second slurries weresubjected to like liquefaction conditions in several repeat experiments.The cyclohexane conversion for the slurry prepared with the 400l550 F.fraction was an average 36.2 weight percent (MAF coal) and that of the550/700 F. fraction was an average 36.3 weight percent (MAF coal).

The results of these liquefactions are summarized below.

Cyclohexane Conversion Wt.

MAF Coal Total Solvent 400l550 F. 50/700 F. 400/700 F. Cut Cut Solvent 123.9 37.8 30.0 Solvent 2 35.2 36.2 36.3

Surprisingly, higher cyclohexane conversions were obtained when slurriesformed with high and low boiling fractions of a solvent were separatelyliquefied than when a slurry formed from the total solvent was liquefiedunder the same conditions. The cyclohexane conversion of each of theparts of the total solventwas greater than the conversion obtained withthe whole total solvent, a totally unexpected effect. Thus, the totalcyclohexane conversion on combining the liquefaction product of the twoparts is greater than obtained with the whole solvent.

Having described our invention, various changes and variations of itwill now occur to those skilled in the art, but insofar as these changesare substantially the same way of accomplishing the same end within thespirit and scope of the appended claims, they are deemed part of theinvention.

We claim:

1. A process for liquefying coal, which comprises:

forming a first slurry of a particulate coal with a low boilingcoal-derived solvent having an initial boiling point of at least about300 F. and a final boiling point within the range from about 500". F. toabout 600 F., and forming a second slurry of such coal with a highboiling coal-derivedsolvent having an initial boiling point within saidrange from about 500F. to about 600 F. and a final boiling point nohigher than about 1,000" F., said final boiling point of said lowboiling solvent and said initial boiling point of said high boilingsolvent being substantially the same, and separately liquefying saidfirst and second slurries under predetermined liquefaction conditions,

whereby the total cyclohexane conversion of said coal in said slurriesis greater than if the coal had been slurried instead in a solventresulting from the admixture of said. low boiling solvent and said highboiling solvent and then liquefied under like liquefaction conditions.

2. The process of claim 1 wherein said low boiling coal-derived solventcontains up to about 10.5 weight percent hydrogen, and wherein said highboiling coalderived solvent contains up to about 9.5 weight percenthydrogen. 7

3. The process of claim 1 wherein said liquefaction conditions include ahydrogen treat rate of from about 0.l to about 6 weight percent hydrogen(MAF coal).

4. The process of claim 1 wherein said liquefaction conditions include:

a temperature within the range from about 700 F. to

about 950 F.,

a pressure within the range from about 300 psig to about 3,000 psig, and

a liquid residence time within the range from about 5 to about 60minutes.

5. A process for liquefying coal, which comprises:

forming a first slurry of a particulate coal with a low boilingcoal-derived recycle solvent having an initial boiling point of at leastabout 300 F. and a final boiling point within the range from about 500F. to about 600 F., and forming a second slurry of such coal with a highboiling coal-derived recycle solvent having an initial boiling pointwithin the range from about 500 F. to about 600 F. and a final boilingpoint no higher than about 1,000 F., said final boiling point of saidlow boiling solvent and said initial boiling point of said high boilingsolvent being substantially the same,

separately liquefying said first and second slurries under predeterminedliquefaction conditions to produce first and second liquefactionproducts,

combining at least the liquids of said first and second liquefactionproducts to obtain a liquid products stream, and

fractionating said liquid products stream to separately recover said lowboiling coal-derived recycle solvent and said high boiling coal-derivedrecycle solvent.

6. The process of claim 5 further comprising:

hydrogenating said liquid products stream under hydrogenation conditionscorrelated to add from about 0.1 to about 5 .0 weight percent ofhydrogen to the liquids in said low boiling coal-derived recycle solventand in said high boiling coal-derived recycle solvent, so that said lowboiling coalderived recycle solvent contains up to about 10.5 weightpercent hydrogen and said high boiling coal-derived recycle solventcontains up to about 9.5 weight percent hydrogen.

7. The process of claim 5 further comprising:

separately hydrogenating said low boiling coalderived recycle solventand said high boiling coalderived recycle solvent under hydrogenationconditions correlated to add from about 0.1 to about 5.0 weight percentof hydrogen to said low boiling coal-derived recycle solvent and saidhigh boiling coal-derived recycle solvent, so that said low boilingcoal-derived recycle solvent contains up to about 10.5 weight percenthydrogen and said low boiling coal-derived recycle solvent contains upto about 9.5 weight percent hydrogen, and

separately recycling the hydrogenated, low boiling coal-derived recyclesolvent and the hydrogenated, high boiling coal-derived recycle solventfor use in forming said first and second slurries.

8. The process of claim 5 in which said liquefaction conditions includea hydrogen treat rate of from about 0.1 to about 6 weight percenthydrogen (MAF coal).

9. The process of claim 5 in which low boiling coalderived recyclesolvent boils from about 400 F. to about 550 F. and contains from about7.5 to about 9.5

weight percent hydro en, and in which said high boilmg coa -der1vedrecyc e solvent boils from about 550 F. to about 700 F. and containsfrom about 7 to about 9 weight percent hydrogen.

10. The process of claim 5 wherein said liquefaction conditions include:

a temperature within the range from about 700 F. to

about 950 F.,

a pressure within the range from about 300 psig to about 3,000 psig, and

a liquid residence time within the range from about 5 to about 60minutes. 11. The process of claim 5 wherein said first and secondslurries are each formed at a solvent-to-coal ratio of from about 0.8:1to about 2:1.

12. A process for liquefying coal, comprising: forming first and secondslurries of a particulate coal 8 mesh (Tyler) and smaller at asolvent-to-coal ratio of about 1.2, the first slurry being formed with alow boiling coal-derived recycle solvent boiling from about 400 F. toabout 550 F., and the second slurry being formed with a highboilingcoal-derived recycle solvent boiling from about 550 F. to about 700 F.,

separately liquefying said first and second slurries under liquefactionconditions including a temperature from about 700 F. to about 950 F., apressure from about 300 psig to about 3,000 psig, and a liquid residencetime from about 5 to about 60 minutes, to produce first and secondliquefaction products,

combining at least the liquids of said first and second liquefactionproducts to obtain a liquid products stream, and

fractionating said liquid products stream to separately recover. saidlow boiling coal-derived recycle solvent and said high boilingcoal-derived recycle solvent.

13. The process of claim 12 wherein said liquefaction conditions includea hydrogen treat rate within the range from about 0.1 to about 6 weightpercent hydrogen (MAF coal).

14. The process of claim 12 wherein said low boiling coal derivedrecycle solvent contains from about 7.5 to about 9.5 weight percenthydrogen and wherein said high boiling coal-derived recycle solventcontains from about 7 to about 9 weight percent hydrogen.

2. The process of claim 1 wherein said low boiling coal-derived solventcontains up to about 10.5 weight percent hydrogen, and wherein said highboiling coal-derived solvent contains up to about 9.5 weight percenthydrogen.
 3. The process of claim 1 wherein said liquefaction conditionsinclude a hydrogen treat rate of from about 0.1 to about 6 weightpercent hydrogen (MAF coal).
 4. The process of claim 1 wherein saidliquefaction Conditions include: a temperature within the range fromabout 700* F. to about 950* F., a pressure within the range from about300 psig to about 3,000 psig, and a liquid residence time within therange from about 5 to about 60 minutes.
 5. A process for liquefyingcoal, which comprises: forming a first slurry of a particulate coal witha low boiling coal-derived recycle solvent having an initial boilingpoint of at least about 300* F. and a final boiling point within therange from about 500* F. to about 600* F., and forming a second slurryof such coal with a high boiling coal-derived recycle solvent having aninitial boiling point within the range from about 500* F. to about 600*F. and a final boiling point no higher than about 1,000* F., said finalboiling point of said low boiling solvent and said initial boiling pointof said high boiling solvent being substantially the same, separatelyliquefying said first and second slurries under predeterminedliquefaction conditions to produce first and second liquefactionproducts, combining at least the liquids of said first and secondliquefaction products to obtain a liquid products stream, andfractionating said liquid products stream to separately recover said lowboiling coal-derived recycle solvent and said high boiling coal-derivedrecycle solvent.
 6. The process of claim 5 further comprising:hydrogenating said liquid products stream under hydrogenation conditionscorrelated to add from about 0.1 to about 5.0 weight percent of hydrogento the liquids in said low boiling coal-derived recycle solvent and insaid high boiling coal-derived recycle solvent, so that said low boilingcoal-derived recycle solvent contains up to about 10.5 weight percenthydrogen and said high boiling coal-derived recycle solvent contains upto about 9.5 weight percent hydrogen.
 7. The process of claim 5 furthercomprising: separately hydrogenating said low boiling coal-derivedrecycle solvent and said high boiling coal-derived recycle solvent underhydrogenation conditions correlated to add from about 0.1 to about 5.0weight percent of hydrogen to said low boiling coal-derived recyclesolvent and said high boiling coal-derived recycle solvent, so that saidlow boiling coal-derived recycle solvent contains up to about 10.5weight percent hydrogen and said low boiling coal-derived recyclesolvent contains up to about 9.5 weight percent hydrogen, and separatelyrecycling the hydrogenated, low boiling coal-derived recycle solvent andthe hydrogenated, high boiling coal-derived recycle solvent for use informing said first and second slurries.
 8. The process of claim 5 inwhich said liquefaction conditions include a hydrogen treat rate of fromabout 0.1 to about 6 weight percent hydrogen (MAF coal).
 9. The processof claim 5 in which low boiling coal-derived recycle solvent boils fromabout 400* F. to about 550* F. and contains from about 7.5 to about 9.5weight percent hydrogen, and in which said high boiling coal-derivedrecycle solvent boils from about 550* F. to about 700* F. and containsfrom about 7 to about 9 weight percent hydrogen.
 10. The process ofclaim 5 wherein said liquefaction conditions include: a temperaturewithin the range from about 700* F. to about 950* F., a pressure withinthe range from about 300 psig to about 3,000 psig, and a liquidresidence time within the range from about 5 to about 60 minutes. 11.The process of claim 5 wherein said first and second slurries are eachformed at a solvent-to-coal ratio of from about 0.8:1 to about 2:1. 12.A process for liquefying coal, comprising: forming first and secondslurrIes of a particulate coal 8 mesh (Tyler) and smaller at asolvent-to-coal ratio of about 1.2, the first slurry being formed with alow boiling coal-derived recycle solvent boiling from about 400* F. toabout 550* F., and the second slurry being formed with a high boilingcoal-derived recycle solvent boiling from about 550* F. to about 700*F., separately liquefying said first and second slurries underliquefaction conditions including a temperature from about 700* F. toabout 950* F., a pressure from about 300 psig to about 3,000 psig, and aliquid residence time from about 5 to about 60 minutes, to produce firstand second liquefaction products, combining at least the liquids of saidfirst and second liquefaction products to obtain a liquid productsstream, and fractionating said liquid products stream to separatelyrecover said low boiling coal-derived recycle solvent and said highboiling coal-derived recycle solvent.
 13. The process of claim 12wherein said liquefaction conditions include a hydrogen treat ratewithin the range from about 0.1 to about 6 weight percent hydrogen (MAFcoal).
 14. The process of claim 12 wherein said low boiling coal derivedrecycle solvent contains from about 7.5 to about 9.5 weight percenthydrogen and wherein said high boiling coal-derived recycle solventcontains from about 7 to about 9 weight percent hydrogen.